Tuning arrangement



Patented Apr. 20, 1948 UNITED- STATES PATENT OFFICE \TUNING ARRANGEMENT Cliflord G. Fick, Schenectady, N. Y., assignor to General Electric New York Company, a corporation of Application August 24, 1942, Serial No. 455,827

ZOIaims. (Cl. 250-33) posite to that presented by the antenna at that frequency, so that the combination of reactance and antenna is series resonant. Such a series resonance combination is capable of developing the high voltage necessary to excite an antenna at a frequency at which it exhibits high reactance and high resistance.

At certain frequencies an antenna exhibits anv inductive reactance which is so great that the extremely low value of capacity required for series resonance cannot be physically realized. Stray capacity from the antenna connection near the transmitter and from the capacity with which the antenna is to be made series resonant are sufiicient in such cases to make the required condenser capacity less than zero. It is accordingly an object of my invention to provide new and improved means whereby an antenna system may be excited efiiciently at a frequency where it exhibits such high inductive reactance.

It is a further object of my invention to provide means whereby the excitation of an antenna under such conditions may be accomplished with simple and easily adjusted tuning means.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. The invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates an antenna tuning circuit embodying my invention; Fig. 2 shows certain impedance characteristics of antennae of the type shown in Fig. 1; and Fig. 3 illustrates certain vectorial. relations existing between the voltages and currents in the circuit depicted in Fig. 1. e

In Fig. 1 an antenna l0, which is shown schematically, is supplied with high frequency power from a radio transmitter ll through a tuning arrangement l2. The output of the transmitter H is impressed across an inductance l3, of which one terminal is grounded, and which is arranged Where a particuin adjustable inductive relation with a second inductance M, of which one terminal is also grounded. The ungrounded terminal of inductance I4 is connected through an adjustable inductance I5 to a movable switch member l6 which cooperates with three stationary contacts l1, I8 and 19. Condensers 20, 2! and 22, of different sizes are connected respectively between fixed contacts I1, I 8 and t9 and a terminal 23 to which the antenna system I!) is connected.

An inductance 24 of very low resistance is connected between the terminal 23 and ground.

- In- Fig. 2 the reactance and resistance char acteristics of antenna systems in generalare illustrated, such characteristics being applicable to any form of the antenna l0. Curve 3!] of Fig. 2 shows the variations in the reactance of an antenna with frequency. For this curve 30, the reactances are plotted as ordinates, inductive reactance being plotted in the positive upward direction, and capacitive reactance being plotted in the downward negative direction. Frequencies are Plotted as abscissae, one unit of frequency being that lowest frequency at which an antenna is resonant. At very low frequencies an antenna is capacitively reactive, as indicated by the portion 3| of curve 30, and at somewhat higher frequencies it becomes inductively reactive, as indi-.

cated by the portion 32 of curve 30. At still higher frequencies, the antenna alternatel be comes eapacitively reactive and inductively reactive, passing through a point of zero reactance; or resonance, each time the sign of its reactance changes.

Curve 33 of Fig. 2 illustrates the variation of resistance of an antenna with changes in frequency. The major part of such resistance is radiation resistance, which is maximum at frequencies where the reactance of the antenna changes sign most abruptly.

According to my present invention, the radio transmitter ll operates at frequencies at which the antenna I0 exhibits large inductive reactance,

as at points along the portion 32 of the curve 30, or at similar portions of the curve 30 at higher frequencies. The inductance 24 has a reactance at the frequency of operation of the transmitter I l which is small relative to the inductive react ance of the antenna H).

In operation, coupling between the inductances l3 and I4 is reduced to avoid overloading of the transmitter H during tuning operation. Switch member I 6 is operated to connect that one of the condensers 20, 2|, 22 in circuit with the adjustable inductance l5 such that adjustment of the inductance 15 may be made to tune the system between the transmitter II and the antenna l and inductance 24 to resonance. After such adjustment is attained, at which the inductance l and one of the condensers 20, 2|, 22 have such values that the system is resonant as a whole, coupling between the inductances l3 and I4 is increased until a suitable load is imposed on the transmitter II.

of course, it should be understood that the tuning means I5 through 22 may be any suitable reactance element or combination of reactance elements suitable for tuning the parallel combination of antenna Ill and inductance 2.4,. Itmay, for example, be a single variable condenser, or if greater range of frequency adjustment isv de- "sired, it may be a plurality of such condensers with suitable switching'means.

The reactance of that one of the condensers 20.2 22 w i h is se c ed a the ar u a ope atin frequency o the ransm tter It mu be larger than the reactance of the inductance 15, so that the net reactance of inductance i5 and that one of the condensers Z0, 21, 22 which is connected in circuit is capacitive. This capacitive reaotance is adjustable by adjustment. of the inductance l5 and serves to tune the entire system.

In Fig. 3 the vector E represents the voltage which appears between the antenna It) and ground. that is, the voltage across, the inductance 24. This voltage, as explained previo iSly, must be extremely high in order to excite the antenna n at a fr q y at. whi h it exhi its extremely high impedance. This high volta e is attained y t t i me ns 5 t rou h 2. The cu re vector I24 represents the current flow through the inductance 24 when the voltage represented by the vector Em exists across it. The vector I o ile lustrates the current flowing into the antenna II] when the voltage represented by the vector E10 xists betwe n the ntenna nd round. The vecor Ila-.22 represents the vectorial resultant of the current vectors Ill) and 1 2 and represents the total current flowing through the tuning means l5 through Since the total current flowing through the tuning means I5 through 22, as represented by the vector Ira-g2, is much larger than the current flowing through the antenna it}, represented by the vector In), the impedance of the parallel combination of inductance 24 and the antenna I0 is much smaller than the impedance of the antenna alone at the particular operating frequency represented by the v ctors of Fi 3. It should be noted that. the vector In makes a much smaller angle with the vector E than does the vector I24, because radiation resistance and the like of the antenna l0 produce a substantial apparent resistance in the antenna It]. It is desirable that current flow throu h the ind tan 24 s u be ar e, nd hat inducta ce sho l be of h h q i r. that is. ts r sistance hould e ery low. so that losses n he nducta ce re a min mumrbe vee or a di g am of F 3 ho s tha he mpedance of t e antenna i e s e in 3 the relation betweenthe vectors I1 and E10, is much greater and is more nearly resistivethan the impedance of the parallel combination of antenna H1 and inductance 24, represented by the vectors 115-2 2 and E10. With the more reactive m dan of the pa a l mbin t n of antenn H! and inductance 24. t e tuning m an l through 2 must appear as a much ar er c peeity, so. that tu ng is greatly s mp fied- Viewed in another way, the inductance 24, placed in parallel to the exciting connections for the antenna [0, acts as a transformer, the inductive reactance of the combination appearing at the connection 23 as a much smaller reactance than if the inductance 24 were omitted from the circuit. Further, the tuning means l5 through 2.7;, together with the inductance 24 in parallel with the antenna ill, have a transformer action such that the voltage in inductances I3 and I4 necessary to excite the antenna i0 is small and the current large, whereby the resistance of the antenna 10 appears smaller, when the inductance 24 is used in parallel to the connections to the antenna l0. Without the inductance 24, the radio frequency current would be vanishingly small and the voltage so high as to make the design of coupling inductances l3-I4 difiicult in view of the necessity of matching the output of the transmitter H to the high reactance and resistance exhibited by the antenna. Such design is especialh; vdiiiicult where the antenna is to be used over a wide frequency range, such that at times the antenna exhibits low reactance and resistance. By my present tuning arrangement includ ing the inductance 2.4, I have simplified the design of the coupling inductances i3 and [4 by reducing the apparent impedance of'the antenna to, as. measured through the tuning means l5 through 22 from the high values the antenna actually assumes at the particular frequencies in question. Of course, the inductance 24, is made no smaJIer than is. necessary to decrease the ap-. parent. inductive reectance of the antenna ID, to a. workable value such that the tuning means l5 through 22 can be. made to tune the antenna prop.- erly and the coupling mean [3, 14, to match the transmitter impedance. to the tuning means and antenna. It is desirable to make the inductance no smaller than necessary in order to minimize inevitable losses in the inductance, which may be minimized by making the resistance of the inductance 24 as small as possible.

While I have illustrated my invention as being used with an antenna radiating radio frequency power, it should be understood that it may be employed with any load circuit into which high frequency energy is to be transferred, which load circuit exhibits high inductive reactance at the frequency of the high frequency energy.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from my invention in its broader aspects, and I, therefore, aim in the a pended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of high frequency energy. a load circuit exhibiting high inductive reactance at the frequency of energy from said source. means fo onne t n said l ad and source and for tuning said load. to the frequency of energy from said source, the inductive reactance of said load being so high, as to require the capacity of said tuning means to be vanishingly small for resonance, and means comprising an inductance connected across said load for reducing the efiective inductive reactance of said load as it appeal-S in combination with said inductance to an inductive reactance sufficiently low that said tunine means s a phr eall real z e c p y.

2. In combination, a source or high frequency ground having an inductive reactance at the fre- 5 quency of energy from said source small relative to the reactance of said antenna, a capacitive reactance connected between said source and the point of connection of said antenna and said inductance, said capacitive reactance being of such value as to resonate the inductive reactance presented to said point by said antenna and said inductance at the frequency of said high frequency energy.

CLIFFORD G. FICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,123,098 Coh'en Dec. 29, 1914 1,551,624 Schelleng Sept. 1, 1925 1,809,630 Kummerer June 9, 1931 1,830,880 Misenheimer Nov. 10, 1931 1,876,971 Kroger Sept. 13, 1932 1,893,136 Franklin Jan. 3, 1933 1,998,322 Kaar Apr. 16, 1935 

